Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/666b5a519a5cf43a8fb80a5cc21d0bf2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563